INSECT ENEMIES OF WESTERN FORESTS 147 
Species of Trypodendron Hosts and distribution 
TEM UOKRCHLUS BS Wee see et Engelmann spruce and _ white-bark pine. 
Idaho and Montana. 
Te pon aderosae ISwee- 2-22 = Ponderosa pine, Engelmann spruce, Douglas 
fir, and mountain hemlock. British Colum- 
bia and south to Oregon. 
me ROLILS ILS) wliG Gas ee ee Bee Poplar and aspen. Western States and 
Canada. 
The oak timber beetles of the genus Pterocyclon (Monarthrum) 
are small, elongate, cylindrical, dark-brown ambrosia beetles which 
work in the wood of oak and various other hardwoods and deciduous 
trees. After the beetles have entered into the wood they excavate 
a central nuptial chamber from which secondary tunnels branch in 
three or four directions. From the secondary branches the larval 
cradles are excavated at right angles and parallel to the grain of the 
wood. Pterocyclon scutellare Lec. (fig. 72), about one-eighth inch 
in length, works in various species of oak from Oregon to southern 
California. P. dentiger Lec. is a smaller species, about. one-sixteenth 
inch in length, which works in the same trees in California. 
Species of Xyleborus make very small pinholes in the dying or 
dead wood of a wide assortment of fruit, shade, and forest trees. 
Larval cradles are not formed, and the tunnels are either plain or 
enlarged into cavities where the larvae feed. Most frequently their 
work is found in dying or recently dead wood. Xyleborus scopu- 
lorum Hopk. works in the dead woed of ponderosa pine and Coulter 
pine in California, Oregon, and South Dakota. X. arbuti Hopk. 
works in madrona in California. X. xwylographus Say is the very 
common eastern species which attacks a large variety of hardwoods. 
Similar species in the Western States have been referred to this spe- 
cies. The galleries consist of simple branching tunnels in which the 
larvae live and feed upon ambrosial fungus without constructing an 
enlarged cavity or larval cradle. 
THE FLATHEADED WOOD BORERS 
(Buprestidae) 
The flatheaded borers have been previously discussed under the 
section on cambium or inner-bark miners (p. 132). By far the larger 
number of species, however, are of more economic importance as 
wood borers than as killers of living trees. Many species work first 
in the inner bark of dying trees, then extend their tunnels into the 
sapwood and even into the heartwood. The flattened oval wormholes 
that are made by the horseshoe-nail-shaped grubs are usually tightly 
packed with boring dust and may wind in a tortuous fashion back 
and forth through the wood so as to riddle it completely. Even a 
few such wormholes greatly lower the quality of the lumber, and a 
large number make it unfit for any but the roughest use. Some of 
these wood borers attack the pitchy fire scars on living trees and 
gradually extend their mines into the sounder portions. Many others 
attack trees that have been killed or felled and do most of their 
damage while the wood is still unseasoned. Others will attack wood 
after 1t has been run through the mill and is placed in storage, or 
even after it has been put into use. 
The prevention of fire scars and other injuries to standing trees 
and the prompt utilization of dead or felled trees will reduce this 
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